The present invention relates to input/output devices. More particularly, the present invention relates to input/output devices for paper-like computing. Still more particularly, the present invention relates to a low power, high resolution display for paper-like computing.
The use and proliferation of portable computing devices has become widespread. In particular, there are a number of small computing devices such as personal digital assistants (PDAs), smart phones, tablet computers, digital cameras, video games and laptop computers that include combined input/output devices. These input/output devices allow the user to interact with the device using a pen or stylus and provide a display for presenting information and input command selections. For example, a prior art system 100 including a pen or stylus 104 and a computing device 102 is shown in FIG. 1. The computing device 102 comprises a touch panel of a conventional type that has a display 106 and a touch sensitive input 108. However, one particular problem for such devices is that the display is typically an active matrix liquid crystal display (LCD), and LCD requires a significant amount of power because the state of each pixel in the display must be maintained by the continuous application of power. Furthermore, much additional power is used to drive backlighting for the LCD panel. Since the devices are often portable, power consumption is a concern and a significant drawback for current devices.
The have been attempts in the prior art to solve power consumption limitations of the prior art with electrophoretic displays, sometimes referred to as electronic paper or electronic ink. Electrophoretic displays have the advantage that an image drawn on such a display is preserved even when the power is removed. Unlike a conventional flat panel display that uses a backlight to illuminate its pixels, electrophoretic displays reflect light like ordinary paper and are capable of holding text and images without drawing electricity or using processor power. Such technology is very popular for electronic books because power is only required to turn a page, not while reading the text on the page. For example, FIG. 2 shows a device 202 with such a paper-like display 204. Electrophoretic displays are typically monochrome. Adding a color filter to the electrophoretic display significantly reduces the contrast and resolution of the display. Another problem with electronic paper or electronic ink or other zero-power display technologies is that the display cannot be updated very rapidly and cannot support motion video rates. Many display modes require the entire display to be refreshed and this takes a long time, thereby limiting the refresh rate to less than one frame per second. It is important to note that interactive user interfaces on computers must be responsive to user requests and delays of more than a second makes the computer seem sluggish and unresponsive and in some ways unusable.